Electronic circuits, such as integrated circuits, are used in a variety of products, from automobiles to microwave ovens to personal computers. Designing and fabricating these circuit devices typically involves many steps, known as a “design flow.” The particular steps of a design flow often are dependent upon the type of integrated circuit being designed, its complexity, the design team, and the integrated circuit fabricator or foundry that will manufacture the circuit. Typically, software and hardware “tools” will verify a design at various stages of the design flow by running software simulators and/or hardware emulators, and errors in the design are corrected.
Several steps are common to most design flows. Typically, the specification for the new circuit initially is described at a very abstract level as a logical design. An example of this type of abstract description is a register transfer level (RTL) description of the circuit. With this type of description, the circuit is defined in terms of both the exchange of signals between hardware registers and the logical operations that are performed on those signals. A register transfer level design typically employs a Hardware Design Language (HDL), such as the Very high speed integrated circuit Hardware Design Language (VHDL) or the Verilog language. The logic of the circuit is then analyzed, to confirm that the logic incorporated into the design will accurately perform the functions desired for the circuit. This analysis is sometimes referred to as “functional verification.”
In some instances, the functionality of the circuit design will be verified by simulating the operation of the design using software. Some designs may be too large or complex to efficiently simulate using software, however. Instead, the functionality of the circuit design will verified by emulating the circuit design using a hardware emulator. Examples of hardware emulators include, for example, the VELOCE family of emulators available from Mentor Graphics Corporation of Wilsonville, Oreg., the ZEBU family of emulators available from EVE SA of Palaiseau, France, and the PALLADIUM family of emulators available from Cadence Design Systems of San Jose, Calif. An emulator typically will provide a set of primitive components for emulating the operation of a circuit design. For example, emulators, some of which may use conventional field-programmable gate array circuits, emulate the functionality of a circuit design using a combination of state elements, memories and lookup tables. Of course, other types of emulators may provide additional or alternate primitive components. For example, alternatively, an emulator may function by using combinatorial elements computing a selectable function over a fixed number of inputs.
As those of ordinary skill in the art will appreciate, emulators are often connected to auxiliary hardware devices, such that during emulation, behavior of the design being emulated and the auxiliary hardware device can be tested. As will be appreciated, this connection is typically facilitated through a bus. As such, conflicts between the emulator and the auxiliary hardware device can arise during emulation, for example, due to bus drivers with incorrect timing. Additionally, when the emulator and the auxiliary hardware device operate on different voltages, a voltage level translator needs to be inserted into the bus, in order to facilitate operability. Conflicts arising from the voltage level translator not operating as expected can also arise during emulation. Furthermore, various auxiliary devices require a period of time in which to warm up prior to operation. If this warm up time is not properly accounted for in the emulation, then conflicts can also arise due to the auxiliary device not being warmed up.